In developed countries including Japan in which the society is aging, age-related diseases show an increasing tendency. Among them, the number of patients with dementia typified by Alzheimer's disease is significantly increasing and has become a major social problem because of involving disturbance in daily life, increased care burden on families or the like, etc.
Incidentally, idiopathic normal pressure hydrocephalus (iNPH; hereinafter, referred to as “iNPH”) is known as a disease that exhibits symptoms similar to those of Alzheimer's disease. According to epidemiological studies, the number of dementia patients in Japan exceeds 3,000,000 people, among which, by estimate, Alzheimer's disease patients account for more than half and idiopathic normal pressure hydrocephalus (iNPH) patients account for 310,000 people. Both the diseases have common symptoms of dementia and ventricular dilatation, but largely differ in that the curative therapy of Alzheimers disease has not yet been established, whereas iNPH is “treatable dementia” that can be cured by operations such as shunting (Non Patent Literature 1). Nonetheless, the number of operations of this shunting remains at yearly 1,200 cases in Japan. Among the 310,000 potential patients, patients who have undergone the operation are only 0.4% on a single-year basis. Examples of the reason therefor include the misdiagnosis of many iNPH patients with Alzheimer's disease because a convenient and reliable diagnosis method to distinguish iNPH patients from Alzheimer's disease patients has not been established.
Although the cause of iNPH is unknown, an excess of spinal fluid caused by the abnormal absorption of spinal fluid is suspected. In iNPH, excessive spinal fluid compress the brain. Thus, a method (tap test) which involves removing a large amount of spinal fluid by lumbar puncture and using the presence or absence of the resulting alleviation of the symptoms of the compressed brain as an index is adopted for the definitive diagnosis of iNPH. This method, however, is highly invasive and also has a high false-negative rate. In addition, since most of iNPH patients are elderly persons, only a small amount of spinal fluid is collected due to lumbar deformity, often making the diagnosis itself impossible. Hence, the development of a reliable diagnosis method to distinguish both the diseases is an important medical theme (Non Patent Literature 1).
To solve these problems, a method which involves searching for a glycoprotein that is contained in a body fluid and is highly correlated with a particular disease, and using the glycoprotein as a diagnostic marker for determining the presence of the disease has received attention in recent years. Most of proteins in body fluids are modified with sugar chains, and these sugar chains often have structures specific for organs, tissues, cell species, or disease conditions of their origins. Specifically, it is known that even the same proteins have distinctive sugar chains when derived from different organs or tissues. Hence, abnormality in a particular organ can be detected by use of a glycan-isoform.
For example, Patent Literature 1 discloses spinal fluid-derived glycoprotein transferrin-1 (Tf-1) (glycan-isoform characteristic of spinal fluid) having a sugar chain containing terminal N-acetylglucosamine (GlcNAc) as a diagnostic marker capable of distinguishing iNPH from Alzheimer's disease (Non Patent Literature 2). The method disclosed therein can distinguish iNPH from Alzheimer's disease with high accuracy by detecting Tf-1 having the sugar chain from spinal fluid. Also, the method can distinguish iNPH from other dementia types such as frontotemporal dementia and dementia with Lewy bodies. Meanwhile, Tf-1 as well as a transferrin isoform having a different sugar chain structure (transferrin-2: Tf-2) is present in spinal fluid. Heretofore, the identification of a protein moiety using an antibody and the identification of a sugar chain moiety using a lectin have had to be carried out in separate steps in order to detect a particular glycan-isoform in the spinal fluid in which these glycan-isoforms coexist with each other. Such a detection method is poorly efficient and is also inferior in rapidness. Further problems thereof are that full automation is difficult due to complicated procedures with many steps and a high-throughput process cannot be achieved.